1. Field of the Invention
The present invention relates to an inlet of blow gun, and more particularly to a metal inlet combined in the plastic blow gun by injection molding the inlet tightly without it being loose and without leakage when it is in use.
2. Prior Art
In accordance with the conventional plastic blow gun, as shown in FIG. 1, the inlet 11 is provided with an internal screw thread 111 for connecting with a quick connector providing the compressed air from the compressed air source. So, the inlet 11 and the internal screw thread 111 are molded with the blow gun, integrally. However, there are some shortcomings existing in this structure, as follows:
1. Due to the physical phenomenon of heat-expansion and cool-shrinking, the cooling of the plastic after stripping from the high-temperature die, the internal screw thread 111 becomes distorted, or the teeth are contracted, so that the tightness of threaded engagement therewith is poor, even causing leakage. PA1 2. Because the internal screw thread 111 is plastic, it is not rigid enough, so that the threaded engagement of the connection will loosen over time, and sometimes the surface of the internal screw thread 111 will be stripped off, causing leakage. PA1 3. During long term use under high pressure with compressed air, the fatigue resistance of the plastic at the internal threaded portion is so short that the service life of the blow gun is affected. PA1 4. Because the plastic has a poor strength and lack of rigidity, the internal screw thread 111 often is cross-threaded when screwing on the quick connector, causing the internal screw thread 111 to be damaged, even causing the inlet 11 to break.
For overcoming the above-mentioned shortcomings, a new blow gun has been brought out on the market, in which a reformed metal inlet 20 is embedded into the trunk of the blow gun, as shown in FIG. 2. The inlet 20 is presented to a cylinder having a ratchet striated outside surface, and a smaller diameter front tip end for embedding an O-ring 22, and a threaded internal screw hole 23. Referring to FIG. 3, a stepped hole 12 is formed at the intake position for embedding the metal inlet 20 therein. The end of the stepped hole 12 is sealed with the O-ring 22 for preventing the compressed air from leaking. Pressing the inlet 20 embeds the ratchet striated surface 21 into the stepped hole 12 for retaining the metal inlet 20 in place, so that the quick connector threads into the metal inlet 20 to overcome the shortcomings of the plastic inlet.
As the embedded inlet 20 is pressed into the plastic blow gun 10, it has an engaging depth of 0.2-0.3 mm, and the meshing strength is thereby very limited. When screwing on the quick connector, and for avoiding leakage and looseness, the threaded joint is often over-torqued with a large turning effort. Often the torque is sometimes so large that the engaging joint between the ratchet striated surface 21 and the plastic trunk of the blow gun causes the metal inlet 20 to slip off and to lose relative function. On the other hand, when pressing the metal inlet 20 into the plastic trunk of the blow gun 10, the central axis of the inlet 20 is often misaligned, so that the O-ring 22 cannot seal the end of the stepped hole well, with the result that the compressed air will leak during long term use under high pressure. Therefore, the service life of this kind of blow gun is not long enough, and the production cost cannot be easily reduced.